1. Field of the Invention
The present invention relates to an image forming apparatus and a fixing device.
2. Description of Related Art
In general, an electrophotographic image forming apparatus (such as a printer, a copy machine, and a fax machine) is configured to irradiate (expose) a charged photoconductor with (to) laser light based on image data to form an electrostatic latent image on the surface of the photoconductor. The electrostatic latent image is then visualized by supplying toner from a developing device to the photoconductor (image carrier) on which the electrostatic latent image is formed, whereby a toner image is formed. Further, the toner image is directly or indirectly transferred to a sheet, followed by heating and pressurization, whereby an image is formed on the sheet.
The above-mentioned image forming apparatus has a problem that the amount of charge of sheets is increased due to the increased speed, increased frequency of duplex printing, and improved image quality, and as a result, the sheets after the fixing step are electrostatically attached to each other. Typically, sheets are charged at a transferring step and a fixing step. In the transferring step, a high voltage is applied to the sheet to electrostatically attach (transfer) a toner image to the sheet. Here, as the basis weight of a sheet is increased, the required amount of voltage is increased, and the surface potential (charging potential) of the sheet is increased. In addition, in the fixing step, a sheet is conveyed while being heated and pressed at the fixing nip, and therefore the sheet is charged by the frictional charge generated between the sheet and the fixing member, and by the peeling charge generated by the peeling of the sheet from the fixing member peel. When sheets after the fixing step are electrostatically attached to each other, the sheets are difficult to align at the time of placing the sheets in a placement tray or the like before aligning the sheets and performing a post process such as a cutting process and a punching process, and this may result in a negative influence on the result of the post processes.
In order to solve the above-mentioned problem, an image forming apparatus has been proposed in which a first discharging brush is provided in a sheet width range except for the portion where an ejection roller is disposed at a sheet outlet, and a second discharging brush is provided in a range of the width of the ejection roller on the downstream side relative to the sheet outlet of the sheet conveyance path (see, for example, Japanese Patent Application Laid-Open No. 10-302993).
In addition, an image forming apparatus has been proposed which includes a first discharger provided in the proximity of a portion on the downstream side of the sheet ejection roller pair, a second discharger provided at an entrance of a sheet guide disposed on the downstream of the first discharger, and a third discharger provided in the proximity of the a portion on the upstream side of the sheet ejection roller pair (see, for example, Japanese Patent Application Laid-Open No. 2006-44907).
In addition, an image forming apparatus has been proposed which includes a sheet pressing member provided with three functions including a function of enhancing the placement of sheet members by guiding the sheet members onto an ejection tray, a function as a detection member for detecting the amount of placed sheet members, and a function of discharging the sheet members (see, for example, Japanese Patent Application Laid-Open No. 2006-306559).
However, in the techniques disclosed in Japanese Patent Application Laid-Open Nos. 10-302993, 2006-44907 and 2006-306559, since only one side of the sheet is neutralized, the electric charge of the sheet cannot be sufficiently removed. That is, the technique disclosed in Japanese Patent Application Laid-Open Nos. 10-302993, 2006-44907 and 2006-306559 cannot sufficiently solve the problem that the sheets after the fixing step are electrostatically attached to each other.